Definition of Internal ear

Internal ear: There are three sections of the
ear. They are the external
ear, the middle ear, and the internal ear. The internal ear
is far and away
the most highly complex. The essential component of the
inner ear for
hearing is the membranous labyrinth where the fibers of the
auditory nerve
(the nerve connecting the ear to the brain) end. The
membranous labyrinth is
a system of communicating sacs and ducts (tubes) filled
with fluid (the
endolymph). The membranous labyrinth is lodged within a
cavity called the
bony labyrinth. At some points the membranous labyrinth is
attached to the
bony labyrinth and at other points the membranous
labyrinth is suspended in
a fluid (the perilymph) within the bony labyrinth.

The bony
labyrinth has
three parts: a central cavity (the vestibule),
semicircular canals (which
open into the vestibule) and the cochlea (a snail-shaped
spiral tube). The
membranous labyrinth also has a vestibule which consists of
two sacs (called
the utriculus and sacculus) connected by a narrow tube. The
utriculus, the
larger of the two sacs, is the principal organ of the
vestibular system
(which informs us about the position and movement of the
head). The smaller
of the two sacs, the sacculus (literally, the little sac)
is connected with
a membranous tube in the cochlea containing the organ of
Corti. It is in the
organ of Corti that are situated the hair cells, the
special sensory
receptors for hearing. The internal ear is also called the
inner ear.